Edge-bonded bi-metallic strip extending from metal plate on shadow mask to stud via spring of substantially smaller cross-sectional area than strip

ABSTRACT

A three point support for a shadow mask screen within the faceplate panel of a color cathode ray tube is provided by three studs embedded in the glass side walls of the panel and spring mounting members which are connected to the studs and to edge bonded bimetallic strips which in turn are connected to the shadow mask. The springs and bimetallic strips are of dissimilar metals, and each spring has a cross-sectional area substantially less than the cross-sectional area of each bimetallic strip thereby thermally insulating the bimetallic strip from the stud of the faceplate panel.

United States Patent.

Palac [54] EDGE-BONDED BI-METALLIC STRIP EXTENDING FROM METAL PLATE ON SHADOW MASK TO STUD VIA SPRING OF SUBSTANTIALLY SMALLER CROSS-SECTIONAL AREA THAN STRIP [72] Inventor: Kazimir Palac, Carpentersville, Ill.

[73] Assignee: Motorola, Inc., Franklin Park, Ill.

[22] Filed: July 9, 1970 [21] Appl. No.: 53,485

[52] US. Cl, ..3l3/85 S, 313/292 [51] Int. Cl. ..H01j 29/06, H01 j 29/08, HOlj 29/02 [58] Field of Search ..3l3/855, 92 B [56] References Cited UNITED STATES PATENTS 3,308,327 3/1967 Shrader ..313/85 S 3,330,980 7/1967 Shrader ..3l3/85 S 3,617,787 11/1971 Plukker ..313/85 S 3,296,625 I/ 1967 Shrader ...3l3/85 S 3,370,194. .622" .SPhflEEEZELflL:-:.T;l2L92L [451 Oct. 24, 1972 3,524,974 8/1970 Kautz ..313/85 S 3,548,235 12/1970 Driedijk et a1 ..313/85 S 3,553,517 l/197l DeBernardis ..313/85 S 3,567,986 3/1971 Bowes et al ..3 13/292 3,573,527 4/ 1971 Hatkenschcid etal ..3l3/292X Primary Examiner-Robert Segal Attorney-Mueller and Aichele 7] ABSTRACT A three point support for a shadow mask screen within the faceplate panel of a color cathode ray tube is provided by three studs embedded in the glass side walls of the panel and spring mounting members which are connected to the studs and to edge bonded bimetallic strips which in turn are connected to the shadow mask. The springs and bimetallic strips are of dissimilar metals, and each spring has a cross-sectional area substantially less than the cross-sectional area of each bimetallic strip thereby thermally insulating the bimetallic strip from the stud of the faceplate panel.

4 Claims, 11 Drawing Figures PAIENTEDncI 24 I972 SHEET 1 0F 2 INVENTOR KAZIMIR PALAC FIGB BY f:

ATTORNEYS.

PNENTEDHBI 24 I972 SHEET 2 OF 2 ATTORNEYS.

BACKGROUND OF THE INVENTION It has been proposed to use edge bonded bimetallic strips in place of CR8 springs to support the shadow mask assembly within the faceplate panel of a color cathode ray tube. Ideally, the springs on either side of the shadow mask will be positioned at an angle with the shadow mask so that upon tube warmup the expansion of the mask will cause the angles the springs make with respect to the mask to change to compensate for the expansion thereby maintaining the center portion of the mask in the same relative position with the center of the screen of light emitting phosphors on the front panel of the tube; As the tube warms up, the edge bonded bimetallic strips then move the shadow mask assembly forward closer to the screen thereby compensating for the radial expansion of the mask to reduce beam landing error. One problem with this type of assembly is that the studs embedded in the face panel of the tube act as radiators to dissipate heat from the bimetal to the outside of the tube so that the bimetal reaction is not directly proportional to the increments of temperature change, therefore the strips do not cause sufficient movement of the shadow mask assembly toward the faceplate panel to completely compensate for beam landing errors. Moreover, when the bimetallic strips. are used to serve both as the angled spring supports and as the means for moving the mask closer to the front panel during tube warmup, unusually long strips are needed, making it difficult to use this type of suspension on mask structures for small screen application due to the limited amount of space for mounting the same.

In addition, the mounting holes in conventional springs are mated with the studs on the front panel in a manner that there is sufficient friction between the stud and the spring such that the shadow mask assembly can become hung up on the studs during tube warm-up thereby preventing proper mask movement about the studs to compensate for beam landing error.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved shadow mask suspension system in a color cathode ray tube, which can readily be adapted for all mask sizes.

It is another object of this invention to provide a shadow mask expansion system for a color cathode ray tube that will respond in a manner directly proportional to the temperature change during tube warmup to move the mask assembly relative to the faceplate panel to accurately reduce beam landing error.

It is a further object of this invention to provide an improved shadow mask suspension system wherein the mask will not become hung up on the mounting studs while correcting for beam landing errors during tube warm-up.

In one particular form of the invention, a cathode ray tube includes a front panel having a discrete pattern of light emitting phosphors thereon. An apertured shadow mask is mounted in the tube in a given alignment with respect to light emitting phosphors by a suspension system which includes a plurality of studs positioned in the front panel. A plurality of substantially straight edge bonded metallic strips are connected at one end to the masking device with the other end extending therefrom in a cantilever fashion. Spring members of a dissimilar metal areconnected' to the extended ends of each of the strips. Each of the spring members have a portion which is adapted to be fastened to a respective stud. In greater details the portion comprises an extruded hole in the spring with the extruded parts making an angle with the stud plane such that the spring engages only the tip of the stud thereby providing minimum surface contact between the two parts. The edge bonded bimetallic strips are responsive to temperature changes in the tube to move the shadow mask about the studs relative to the front panel to reduce electron gun beam landing errors on the light emitting phosphors. The spring members have a cross-sectional area which is substantially smaller than the cross-sectional area of each of the bimetallic strips thereby providing substantial thermo isolation of the spring member from the stripto prevent radiation of heat from within the tube to the outside thereof through the stud members, and the extended holes in the springs limit the friction generated between the springs and the studs during warm-up to prevent the mask from becoming hung up on the studs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of a tri-beam cathode ray tube;

FIG. 2 is a sectional view along the line 2--2 of FIG. 1 illustrating a faceplate panel and shadow mask structure in accordance with one embodiment of the invention;

FIG. 3 is a greatly enlarged representation of a portion of the mask and screen of FIG. 2;

FIG. 4 is a top plan view of one of the devices used in the suspension of the shadow mask structure in the front panel of the tube in accordance with one embodiment of this invention;

FIG. 5 is a side elevation view of the device of FIG. 4;

FIG. 6 is a top plan view of another device similar to that of FIG. 4 which is used in the suspension of the shadow mask structure in the faceplate panel in accordance with one embodiment of this invention;

FIG. 7 is a top plan view illustrating in phantom the operation of the device of FIG. 6 in accordance with this invention;

FIG. 8 is a side elevation view of the device of FIG. 6.

FIG. 9 is a perspective view of an edge bonded bimetallic strip in accordance with one embodiment of this invention;

FIG. 10 is a plan view of a portion of a mounting spring in accordance with one embodiment of the invention; and

FIG. 11 is a cross-section view in elevation along the line 11-11 in FIG. II) and including a portion of a mounting stud.

DETAILED DESCRIPTION Cathode ray tube 10 of FIG. 1 includes a faceplate panel 12 joined to a funnel portion 14 which merges into a tube neck 16. Suitable connectors for the electrodes within the tube project from the tube base 17. In accordance with known color picture tube construction, the neck 16 includes three different electron guns each producing a beam associated with the production of one of three colors making up the composite image.

In FIG. 2, the faceplate panel 12 contains within its rearwardly projecting walls a lightweight shadow mask assembly including the apertured mask 20 and integral frame portion 22. The mask 20 includes apertures 23 (FIG. 3) each of which is precisely aligned with a triad of phosphor dots F, B and G of FIG. 3. The phosphor dots are deposited in accordance with known techniques on the backside of the face of panel 12. As can be understood by consideration of FIG. 3, the approach angle of an electron beam directed at the mask 20 results in one beam striking only the dots marked B to produce the blue light and the other two beams similarlystriking the dots marked R and G to produce respectively red and green lights. As previously stated relative energization of dots in each triad will produce a picture element of desired color.

The shadow mask 20 is mounted within the faceplate panel 12 by a suspension system which includes cantilever mounting members or springs 25, 26 and 27. The springs -27 are each apertured at their free ends such as shown at 28 (FIG. 4) and these apertures fit over the respective mounting studs 30, 31 and 32 which are embedded in the glass of the front panel 12. The ends of the spring members opposite to the apertured ends are connected to substantially straight, edge bonded bimetallic strips 37 38 and 39 by welds such as shown at 34 (FIG. 4). The edge bonded bimetallic strips in turn are connected by spot welding, for instance, to CRS plates 40, 41 and 42 that are connected to the integral frame 22 of the shadow mask assembly 20 by welding, for instance. The plate 42 shown in FIG. 4 is connected to the right hand side of the shadow mask assembly as viewed from behind in an operating installation, and the plate 41 is connected to the opposite side thereof. The plate 40 is connected to the top of the mask. Because this is a lightweight mask assembly where the ,frame is an integral part of the screen, the walls of the frame are not strong enough to directly support the spring and bimetallic strip if the assembly were welded directly to the mask. Therefore, the plates 40-42 are welded to the frame and the spring and bimetallic strips are then welded to the plate so that the entire assembly is strong enough to pass various drop test requirements.

In FIG. 1 the longitudinal axis 50 is intended to represent an imaginary line intersecting the vertical radial axis 52 and the horizontal radial axis 54 (FIG. 2) which divide the mask and faceplate assembly into four substantially equal quadrants. Since relatively wide spacing of the springs 25, 26 and 27 afford improved mechanical support of the shadow mask, it is preferable that the springs 25 and 27 be connected to the shadow mask in different quadrants from one another and different from the quadrant in which spring 25 is secured to the mask. However, when this nonsymmetrical spacing is used for providing mechanical stability, it results in poor registry of the electron beams passing through the apertures 23 for their intended phosphor dots (FIG. 3), due to the increased non-radial thermoexpansion of the metallic mask with respect to the longitudinal axis 50. In order to maintain the central portion of the shadow mask screen in the same predetermined position with respect to the phosphor pattern on the front panel during tube warmup so mask expansion is purely radial, each of the springs 26 and 27 on either sideof the shadow mask are connected to the mask at a predetermined angle such as at 62 in FIG. 2. This triangulation method for establishing pure radial expansion of a shadow mask screen during tube warmup is described in more detail in U.S. Pat. No. 3,452,234, issued June 24, 1969, and assigned to the same assignee as this application. In this type of suspension system, the stud 30 at the top of the front panel is mounted at the end of the central vertical axis 52, and the spring 25 is held substantially parallel to the shadow mask 22 so that the spring 25 creates a minimal shift of the shadow mask on the order of 0.0001 to 0.0002 inch, which for all practical purposes can be ignored.

During tube warmup in an operating installation, the shadow mask expands outwardly causing the angle that each of the springs 26 and 27 makes with the shadow mask screen to change as heretofore described thereby causing the mask expansion to be purely radial. At the same time, the bimetallic strips 37, 38 and 39 at the top and on each side of the mask respectively react to the temperature change and shift laterally in a linear manner such as shown in phantom in FIG. 4 for the side support and FIG. 6 for the top support. Since the stud fixes the end of each of the springs 25, 26 and 27, the end resultof the lateral movement of the bimetal is the shifting of the entire shadow mask assembly forward to compensate for the change in beam landing on the screen due to the outward radial expansion of the mask. Correction for beam landing error by shifting the mask relative to the screen during tube warmup is described in more detail in application Ser. No. 761,732, filed Sept. 23, 1968, and assigned to the same assignee as this application.

By referring to the elevation and plan views, of the side mounting springs and top spring, FIGS. 4, 5 and FIGS. 6, 7 respectively, one can see that while the width of the spring 27, for instance, (FIG. 4) is substantially the same as the width of the bimetallic 39, the thickness of the spring 27 is greatly reduced over the thickness of the spring 39 (FIG. 5), resulting in the cross-sectional area of the spring being much less than the cross-sectional area of the bimetallic strip. In one operating installation the cross-sectional area of each of the bimetallic strips was on the order of 0.020 square inch, while the cross-sectional area of each spring was on the order of 0.009 square inch. By selecting the spring of a dissimilar metal such as A286-stainless steel and greatly reducing its cross-sectional area comparedto the bimetallic, the spring acts to thermally isolate the bimetallic strips 37 38 and 39 from the respective studs 30, 31 and 32 thereby greatly reducing the amount of heat radiated from the shadow mask through the studs outside the tube. Without this thermal isolation, heat would be radiated from the bimetallic strips through the studs such that the response of the bimetallic strips to tube warmup would not be directly proportional to the increments of temperature change within the tube so the mask would not be shifted forward the proper amount to compensate for beam landing error.

As shown in FIG. 4 which is representative of each of the support devices, the bimetallic strip 39 is connected to plate 42 by two spot welds at 72 and 73 and by a third weld 75 on the extended portion 70. This third weld 75 in effect anchors the bimetallic to the support plate and prevents the whole strip from shifting as a result of temperature change. For instance, if the bimetallic strip were rectangular in shape and had two pairs of spot welds similar to 72, 73 to anchor it, movement of the two dissimilar portions of the bimetallic strip during temperature changes would have a mechanical effect on the spot welds directly opposite one another and cause the whole strip to be shifted on the mounting plate 42, thus causing the mark not to return to its original position. Spot weld 75, therefore, on the extended portion 70 serves as an anchor to the entire bimetallic strip, and prevents the shifting of the strip on the plate.

The location of the welds on the bimetal strips must be extremely accurate since the linear displacement D of the bimetal is directly proportional to the length L (FIG. 9) in accordance with the following formula:

D= (K ATL M)/t where K deflection constant AT= change in temperature of bimetal in F.

M specific deflection lc rate of deflection under load vs. free deflection t thickness of bimetal In order to accurately locate the welds, projections 85 85d are punched into the bimetal to produce a raised area at the point where the welds are to be located. Boss portions 82 are formed on each of the mounting plates 41 and 42 to act as a bearing surface for the bimetallic strips 38 and 39. If the whole bottom surface of each of the bimetallic strips were permitted to rest against the mounting plate, the friction between the two surfaces would be very great thereby making it difficult for the strip toproperly shift across the plate during tube warmup. The boss portions therefore serve as a bearing surface such that the bimetallic strips can accurately respond to the temperature changes to move across the plate and shift the mask.

The boss portions also serve as reference points to determine the angle the spring makes with the mask. That is, as has been previously explained, the angles that the springs 26 and 27 make with the shadow mask 22 are selected such that during tube warmup the angles will change to provide purely radial expansion of the shadow mask. However, as can be seen in FIG. 5, the bimetallic strip 39 is connected in cantilever fashion to the plate 42 which in turn is connected to the wall of the shadow mask. When the mask is mounted into the front panel, the springs are compressed and this action works to force the bimetallic strip against the mounting plate 42, thereby making it very difficult to determine the spacing between the base 80 of spring 27 and the shadow mask wall in a completed installation. Without knowing the exact spacing between the base of the spring or the point where it can be said the spring effectively joins the mask and the shadow mask wall in an operating installation, makes it difficult to select the proper angle that the spring must make with the shadow mask to provide the desired compensation.

To remove this objection, bosses 82 serve as a reference point for determining the angle the spring will make with the shadow mask wall. As can be seen in FIG. 5, when the shadow mask is assembled into the front panel, the bimetallic strip 39 will move into contact with the boss portions such that the spacing between the plate 42, hence the shadow mask wall, and the base 80 of spring 27 can be accurately determined. Knowing this dimension it is asimple matter to calculate the proper angle that the spring must make with the mask wall.

ln-various color tube assemblies efforts to reduce beam landing errors caused by shadow mask expansion during tube warmup by moving the mask about the mounting studs relative to the front panel have been frustrated to some extent by friction between the stud and the walls of the spring defining the periphery of the hole used to mount the spring to the stud. Capitalizing on the lightweight of the shadow mask assembly used in the preferred embodiment of this invention, I developed a uniquely shaped hole in the springs as shown in FIGS. 10 and 11 which for all practical purposes eliminates shadow mask hang up on the studs due to friction. The main thrust of the idea is to extrude the hole in the spring end. The extruded portions 90, 91 and 92 are formed at an angle 0 with respect to the stud plane 94 which angle is on the order of 20. Therefore, the extruded portions forming the hole only engage the tip of the stud such that only negligible friction is generated between the stud and the spring with the shadow mask being moved about the studs during tube warmup.

What has been described, therefore, is a new and unique suspension system for a shadow mask within the front panel of a cathode ray tube which will respond in a manner directly proportional to temperature change during tube warmup to move the mask assembly relative to the faceplate panel to accurately reduce beam landing error.

Iclaim:

l. A color cathode ray tube having an enclosing envelope including a funnel portion and a faceplate panel having a plurality of phosphor dot triodes deposited thereon, including in combination, a shadow mask device, first, second and third studs respectively mounted at the top and on each side of said faceplate panel, means for suspending the mask device from the studs in a spaced relation to the front panel, said means including three substantially straight edge bonded bimetallic strips, connecting means connecting each strip to the top and each side of the mask device, said connecting means including a metal plate connected to said shadow mask, each said bimetallic strip being fastened at one end to said metal plate, a spring member connected to the unconnected end of each said strip, each said spring member having a portion adapted to be fastened to a respective stud, said edge bonded bimetallic strips being responsive to temperature changes in the tube to move the shadow mask relative to the front panel to reduce electron gun beam landing errors on the phosphor dot triodes, and each said spring member having a cross-sectional area substantially smaller than the cross-sectional area of each said edge bonded bimetallic strip thereby providing substantial thermal isolation of each said bimetallic strip from the respective studs thereby enhancing the response of said bimetallic strips to temperature changes to accurately position the shadow mask relative to the front panel.

2. The color cathode ray tube of claim 1 further including, embossed means in each of said metal plates connected to each side of the shadow mask, said embossed means providing a bearing surface for said bimetallic strip to move about in response to temperature changes in the mask thereby insuring a sensitive response of said strip to temperature changes to move the shadow mask to accurately correct for beam landing error.

3. The cathode ray tube of claim 1 wherein each said bimetallic strip is formed from two edge bonded dissimilar metal portions, one said portion extending longer than the other said portion at said one end of said bimetallic strip connected to the masking device, and said means connecting said one end of said bimetallic strip to the masking device includes first and second spot welds adjacent each other on respective dissimilar metal portions, and a third spot weld on said extended portion to anchor said bimetallic strip in position on said metal plate and to the masking device.

4. The cathode ray tube of claim 3 wherein each said bimetallic strip includes projections punched therein to mark the position for said spot welds. 

1. A color cathode ray tube having an enclosing envelope including a funnel portion and a faceplate panel having a pluralitY of phosphor dot triodes deposited thereon, including in combination, a shadow mask device, first, second and third studs respectively mounted at the top and on each side of said faceplate panel, means for suspending the mask device from the studs in a spaced relation to the front panel, said means including three substantially straight edge bonded bimetallic strips, connecting means connecting each strip to the top and each side of the mask device, said connecting means including a metal plate connected to said shadow mask, each said bimetallic strip being fastened at one end to said metal plate, a spring member connected to the unconnected end of each said strip, each said spring member having a portion adapted to be fastened to a respective stud, said edge bonded bimetallic strips being responsive to temperature changes in the tube to move the shadow mask relative to the front panel to reduce electron gun beam landing errors on the phosphor dot triodes, and each said spring member having a cross-sectional area substantially smaller than the cross-sectional area of each said edge bonded bimetallic strip thereby providing substantial thermal isolation of each said bimetallic strip from the respective studs thereby enhancing the response of said bimetallic strips to temperature changes to accurately position the shadow mask relative to the front panel.
 2. The color cathode ray tube of claim 1 further including, embossed means in each of said metal plates connected to each side of the shadow mask, said embossed means providing a bearing surface for said bimetallic strip to move about in response to temperature changes in the mask thereby insuring a sensitive response of said strip to temperature changes to move the shadow mask to accurately correct for beam landing error.
 3. The cathode ray tube of claim 1 wherein each said bimetallic strip is formed from two edge bonded dissimilar metal portions, one said portion extending longer than the other said portion at said one end of said bimetallic strip connected to the masking device, and said means connecting said one end of said bimetallic strip to the masking device includes first and second spot welds adjacent each other on respective dissimilar metal portions, and a third spot weld on said extended portion to anchor said bimetallic strip in position on said metal plate and to the masking device.
 4. The cathode ray tube of claim 3 wherein each said bimetallic strip includes projections punched therein to mark the position for said spot welds. 